Both integrals \(I_{\pm }\)  in (REF ) diverge, but can be regularized using,
for example, zeta regularization [1]}. Following the usual method, we
start by considering the integral,
\(\int _{u\left( 0\right) }^{\infty }u^{-s/2}~du=-\frac{u\left( 0\right)^{1-s/2}}{1-s/2},\quad \operatorname{Re}\left( s\right) >2~. \) 
